The present invention relates to a novel apparatus and method for separating heterogeneous particles in liquid medium.
Particles suspended in a liquid, migrate when subjected to an electric field produced by passing a current through the suspension. Such particles may be interpreted to include ions, molecules, such as protein molecules, or colloidal particles such as kaolin. The speed of migration per unit of electric field strength inside the slurry or suspension is called the electrophoretic mobility of the particle. Particles, colloidal, molecular or ionic, are also motivated due to the mean flow or convective flow of the particle-liquid mixture. In this case, the particles tend to act as fluid material points. The imposition of an electric field on particles subject to a mean or convective flow should, ideally, result in the motion of the particles being of the linear sum of the motions, thereof due to the electric field and the mean flow. Unfortunately, application of an electric field can cause inhomogeneous heating, chemical reactions, and other effects which upset expected flow patterns. Thus, there is a complex interaction between the electric field strength and the motion of fluids subjected to imposed electric fields. In the past, attempts have been made to suppress this complex interaction (thermal convective motion) by applying an electric field inside a porous medium such as a gel. Since these gels have zero convective velocity, which particle species are separated solely by the effect of the electric field imposed i.e.: by virtue of such particles different electrophoretic mobilities and sizes.
U.S. Pat. No. 4,323,439 to O'Farrel describes a system in which a carrier fluid is forced through a chromatography matrix found in a packed column. In addition, a current is imposed on a packed column to employ electrophoretic mobility and size characteristics of the particles for the purpose of separation. A target species is then held inside the column while the other molecular species are driven out of the column by the mean flow or by the electric field.
U.S. Pat. No. 4,107,026 to Freeman describes an electrofiltration apparatus where a membrane is used in conjunction with an electric field to separate colloidal particles from small molecules in water. The membranes shown are non-retentive i.e. the colloidal particles (Kaolin) will easily pass through the pores of the membrane driven by a pressure gradient across the membrane. However, the colloidal particles would be retained by the membrane when an electric current is passed through the pores of the membrane, in opposition to the convective forces prior described. As a result, water and small ions pass through the pores of the membrane while the highly charged colloidal particles are held back, resulting in a separation of the ions from the colloidal particles.
U.S. Pat. No. 4,204,929 to Bier shows a device having a number of chambers formed by a separated parallel membranes. A different pH is imposed on each chamber. An electric field is also applied across the chambers to induce electrophoretic movement of the materials. Proteins, or other biological materials, migrate from one chamber to another until they reach a pH value which counteracts the electrophoretic mobility. At this point, the proteins stop. Thus, a "banding" of biological materials is achieved. However, the Bier system requires the establishment of a separate pH in each chamber which is very difficult and expensive to achieve.
An article by Custler in a text entitled "Bioseparation" theorizes an unstudied concept of using convective flow counter current to electrophoretic motion to obtain particle separation.
A separator for particles in a fluid, utilizing the principles of electrofiltration and electrophoresis, which is accurate, relatively inexpensive and easily controllable would be a great advance in the art of chemical separations.